A. Field of the Invention
This invention relates to methods and apparatus for the remote measurement of the salinity of large bodies of water.
B. Description of Prior Art
Salinity is typically measured by laboratory analysis of an actual sample of water from the body under investigation. For example, the water may be evaporated and the salt residue weighed. As an alternative method, the water may be titrated with silver nitrate to precipitate silver chloride (or metallic silver, upon exposure to light) which may be filtered out and weighed.
In many applications, however, it is not possible to take a sufficient number of samples of the water for adequate testing and analysis. The commonest example of such a situation is where a large body, such as a gulf, is subjected to salinity mapping. In situations such as this, a remote salinity sensing method and apparatus would be quite useful.
There exists a microwave remote salinity analysis technique. Here, thermal emissions from the body of water are remotely sensed in the microwave band from a satellite or high-flying aircraft. Mathematical methods exist for the computation of salinity if the water temperature and surface roughness are known.
However, numerous difficulties have been encountered is using this prior art method. For example, since thermal emissions form the basis for the measurement, the temperature of the water is quite critical and must be measured with great accuracy if usable results are to be obtained from the salinity calculations. Furthermore, since a microwave source emits at a much lower frequency than a visible light source, the microwave antenna must be rather large to avoid signal-to-noise problems.